Manufacture of aromatic hydrocarbons



May 7, 1946.

G. B. ARNOLD 2,399,780

MANUFACTURE OF AROMATIC HYDROCARBONS Filed July 9, 1942 CATALYTICCONVERSION BENZENE EXCHANGE REACTION MOTOR FUEL t 1 |9- l3 FRACTIONATE|5- HIGHER XYLENE BENZENE BOILING FRACTION R i TOLUENE g I BENZENE 2.0 i

CATALYTIC CONVERSION (BENZENE EXCHANGE REACTION).

GEORGE B. ARNOLD 11v VENTOR HIS A TTORNE Y Patented May 7, 1946MANUFACTURE OF ABOMATIC HYDBOCABBONS George B. Arnold, Beacon, N. 2.,aaaignor to The Texas Company, New York, N. Y., a corporation ofDelaware Application July 9, 1942, Serial No. 450,253 .6 Claims. (c1.260-668) This invention relates to the treatment of hydrocarbons,particularly petroleum hydrocarbons for the production of highlyaromatic motor fuels as well as toluene.

The invention relates to a process in which higher boiling aromatichydrocarbons in the presence of benzene and in contact with a suitablecatalyst are subjected to a conversion involving an exchange reactionbetween benzene and higher boiling aromatic hydrocarbons to form lowerbolling aromatic hydrocarbons within the gasoline boiling rangeincluding toluene. In accordance with the invention petroleum stockscontaining aromatic hydrocarbons are subjected to catalytic conversionin the presence of benzene, the products of conversion are fractionatedto separate the lower boiling products from a higher boiling tractionand such higher boiling fraction is subjected either to a secondcatalytic conversion operation in the presence of benzene or issubjected to cracking or conversion to produce lower boiling productsadapted for the exchange reaction operation.

The invention will be understood by reference to the accompanying flow.diagram which represents diagrammatically a particular embodiment of theinvention.

The charging stock comprising a gasoline or naphtha stock is introducedthrough a line 9 together with benzene, admitted through line III, to' acatalytic conversion step I l. The charging stock is preferably anaphtha stock containing aromatic hydrocarbons and having an initialboiling point of about 250-310 F. and 'an end point of 400 F.-500 F.Since the amount of aromatic hydrocarbons in the naphtha fractions ofmost crude petroleums is quite low the charging stock will generally bea product from a previous conversion process such as naphtha stocksproduced by thermal or catalytic or reformed or aromatized naphthastocks. A very suitable stock may comprise the higher boiling productsproduced in the so-called hydroforming process in which a straight rungasoline stock is subjected'to conversion temperatures of about 900lit-1000 F. in contact with an aromatizing catalyst such asmolybdena-alumina and chrome-alumina while in the presence of hydrogenand under 'superatmospheric pressures such as 200-400 p. s. i.

In the catalytic conversion step II the mixture of benzene and higherboiling stock is raised to a conversion temperature of the order of 800F.- 1000 F. in contact with a catalyst adapted to promote conversioninto lower boiling hydrocarbons and promote an exchange reaction betweenbenzene and higher boiling homologs thereof to form lower boilinghydrocarbons in the gasoline boiling range. In the conversion operationhigher boiling aromatic hydrocarbons consisting essentially of dlalkyl,trialkyl or polyalkyi aromatics or longer chain monoalkyl hydrocarbonsare converted to lower boiling hydrocarbons boiling within the gasolineboiling range and an exchange reaction occurs between benzene and higherboiling aromatic hydrocarbons to produce alkyl benzenes in the gasolineboiling range including toluene.

Certain synthetic silica-alumina and aluminum-containing catalysts servethe function of catalyzing the conversion into lower boilinghydrocarbons as well as the exchange reaction between benzene and higherboiling homologs thereof to selectively produce toluene. A syntheticsilica-alumina catalyst is recommended as a superior catalyst foraccomplishing this two-fold purpose. This catalyst may be prepared byprecipitating a mixed gel of silica and alumina and may containadditional reactive agents such as zirconia and thoria. The catalystshould be substantially free from alkali metal. Metallic fluorides suchas aluminum magnesium and chromium fluorides dispersed on adsorptivecarriers or inorganic gels such as silica and silica alumina gels arealso adapted to function as catalysts for this two-fold purpose. Suchcatalysts are disclosed in the pending applications of Preston L.Veltman and Arthur R. Goldsby, Serial No. 311,- 942, filed December 30,1939, and Preston L. Veltman, Serial No. 311,943, filed December 30,1939, and Serial No. 379,483, filed February 18, 1941. Another suitablecatalyst comprises aluminum phosphate having dispersed thereon a solidmetallic fluoride such as aluminum fluoride, magnesium fluoride andchromium fluoride as disclosed in the pending application of Preston L.Veltman, Serial No. 313,759, filed January 13, 1940, now Patent2,301,913. The pending applications referred to contain detaileddisclosures of these catalysts and reference may be had thereto fordetailed descriptions of the catalysts and the methods of preparingthem. The catalysts employed in my invention may be in the form ofstationary or moving beds of pulverulent or pelleted metal through whichthe hydrocarbon vapors are passed or in a powdered or finely dividedform used as a-slurry or in suspension as in the so-called fluid type ofcatalytic cracking operation.

The mixture charged to the catalytic conversion and benzene exchangereaction step ii may be composed of about 0.2-8.0 volumes of benzene to1 volume of naphtha stock. The mixture is subjected to temperatures ofthe order of 800 F.-

1000 F. at space velocities of the order of 0.1 up to 5.0 to 10, thespace velocity being defined as the liquid volume per hour per spacevolume of catalyst. For the production of toluene there appears to be noadvantage in the use of temperaturesabove 1000 F. at space velocities ofabout 1 but when merely a motor fuel product is desired temperaturesabove 1000 F.may be employed. The operation may be conducted under awide range of pressure such as relatively low pressures of the order to50200 p. s. 1. up to higher pressures such as 400-600 p. s. i. or evenhigher pressures. In the reactions occurring in the presence of thecatalyst higher boiling hydrocarbons are converted into lower boilinghydrocarbons, polyalkyl aromatic hydrocarbons being converted to lowerboiling aromatic hydrocarbons and an exchange reaction takes placebetween the benzene and certain of the aromatic hydrocarbons,particularly aromatics of intermediate boiling range such as thexylenes, to effect the formation of lower boiling aromatics in thegasoline boiling range including toluene. When directing the operationspecifically for the production of toluene the operation ischaracterized by an overall disappearance of higher boiling aromaticsand by a net conversion to toluene and consumption of benzene.

The reaction products pass through line l2 to a fractionating step [3wherein the products are fractionated to obtain the fractions desired.

Thus the products may be fractionated to obtain a benzene cut withdrawnthrough line H, a toluene out withdrawn through line I5, an intermediateboiling range cut withdrawn through line I6 and a higher boilingfraction withdrawn through line II. when it is desired to recovertoluene it is advantageous to recycle the benzene cut through line it tothe conversion step Ii and to pass the fractions boiling above tolueneto the subsequent conversion operation. When making a motor fuel cut,which may be withdrawn through line is, such cut may include the benzeneand toluene fractions or if desired the benzene fractions may beseparately recovered and recycled to the conversion step ll.

The fractions higher boiling than the motor fuel cut withdrawn throughline l9, or higher boiling than the toluene cut withdrawn through line15, are directed through lines It and II to a catalytic conversion step20. In this step the higher boiling fractions from the preceding benzeneexchange reaction step are subjected to a catalytic conversion eitherwith or without benzene. When operating with benzene, makup benzene maybe directed through line 2| to the conversion step 20 and benzene fromthe fractionating step ii may, if desired, be passed through a branchline 22 for introduction to the catalytic cracking step 20. In thisoperation a mixture of benzene and higher boiling fractions aresubjected to conversion conditions similar to those described for theconversion step I l to eflect conversion into lower boiling hydrocarbonsand produce an exchange reaction between benzene and higher boilingalkyl aromatics. By carrying on the benzene exchange reaction in twostages higher conversions to lower boiling aromatic hydrocarbonsincluding toluene may be produced than can be accomplished in a singlestage. The reaction products may be passed through a line 23 to thefractionating step II for fractionation together with the products fromthe conversion step I I.

When operating without added benzene in the conversion step 20 theoperation is preferably carried on in the presence of a catalyst adaptedto promote conversion into lower boiling hydrocarbons and particularlyinto aromatic hydrocarbons adapted for the benzene exchange reaction.Aluminum fluoride, magnesium fluoride and chromium fluoride may bementioned as catalysts which are particularly adapted for use in step20, since these catalysts have the peculiar property of promoting aselective conversion to benzene and thus serve to provide benzene forthe conversion step II. The operation is preferably conducted attemperatures of the order of 900 F.-1100 F., under superatmosphericpressures, such as -400 p. s. i.

In an alternative operation in accordance with the invention thefractionation is so conducted in the fractionating step I3 as toseparate a fraction of intermediate boiling range, includingparticularly the xylenes, from the higher boiling products and torecycle this intermediate fraction, as withdrawn through line l6,through the line 2| to the conversion step ii, while directing thehigher boiling products withdrawn through line H to the conversion step20. In this operation it is advantageous to subject the higher boilingfraction which is directed to the conversion step 20 to catalyticcracking in the absence of added benzene under conditions favorable forthe conversion of the higher boiling hydrocarbons into lower boilinghydrocarbons, particularly aromatic hydrocarbons. The use of thefluoride catalysts, which have been mentioned as promoting a selectiveconversion to benzene, is highly advantageous in this operation in viewof the relatively large yields of benzene produced. The recycling of theintermediate fraction containing xylenes to the benzene exchangereaction step ii is particularly advantageous because the xylenes aremore eflective in the exchange reaction with benzene to produce toluenethan higher boiling aromatics, since the :wlenes by reacting moleculefor molecule with benzene produce two molecules of toluene while thehigher boiling aromatics react molecule for molecule with benzene togive one molecule of toluene.

While I have described a particular embodiment of my invention forpurposes of illustration, it should be understood that variousmodifications and adaptations thereof which will be obvious to oneskilled in the art, may be made within the spirit of the invention asset forth in the appended claims.

I claim:

1. In the manufacture of toluene the process that comprises subjecting amixture of benzene and hydrocarbon 011 containing aromatic hydrocarbonshigher boiling than toluene to catalytic conversion in a conversion zoneto effect conversion into lower boiling hydrocarbons and produce anexchange reaction between benzene and higher boiling homologs thereof tothereby consume benzene and effect selective conversion to toluene,fractionating the resultant products of conversion to sepa te lowerboilin fractions cluding toluene from higher boiling fractions,subjectingsuch higher boiling fractions to catalytic cracking in asecond conversion zone in contact with a metallic fluoride catalyst toeffect selective conversion to benzene, fractionating resultant crackedproducts of the latter con- !6 version to obtain a benzene fraction andrecyaaoavso 3 cling said benzene fraction to the first mentionedcatalytic conversion zone.

2. In the manufacture of toluene the process that comprises subjecting amixture of benzene and hydrocarbon oil containing aromatic hydrocarbonshigher boiling than toluene to eatalytic conversion in a conversion zoneto effect conversion into lower boiling hydrocarbons and produce anexchange reaction between benzene and higher boiling homologg thereof tothereby consume benzene and effect selective conversion to toluene,fractionating the resultant products of conversion to obtain fractionscomprising benzene, toluene, xylene fractions and a higher boilingfraction containing aromatic hydrocarbons, subjecting said higherboiling fraction to catalytic cracking in a second conversion zone incontact with a metallic fluoride catalyst to effect conversion intolower boiling aromatic hydrocarbons comprising benzene and xylenes,fractionating the resultant product of conversion from the latterconversion operation and recycling benzene and xylene fractions to thefirst mentioned catalytic conversion zone.

3. In the manufacture of toluene the process that comprises subjecting amixture of benzene and hydrocarbon oil containing aromatic hydrocarbonshigher boiling than toluene to eatalytic conversion in a conversion zoneto effect conversion into lower boiling hydrocarbons and produce anexchange reaction between benzene and higher boiling homologs thereof tothereby consume benzene and effect selective conversion to toluene,directing the resultant'products of conversion to a fractionating zonewherein fractionation takes place to separate fractions comprisingbenzene, toluene, and higher boiling hydrocarbons, directing the higherboiling hydrocarbon fraction to a second conversion zone wherein thehydrocarbons are subjected to eatlvtie cracking in contact with 'ametallic fluoride catalyst to effect conversion into lower boilinhydrocarbons, directing the resultant products of conversion to saidfractionating zone and recycling the benzene fraction to the firstmentioned conversion zone.

4. In the manufacture of toluene the process that comprises subjecting amixture of benzene and hydrocarbon oil containing aromatic hydrocarbonshigher boiling than toluene to eatalytic conversion in a conversion zoneto effect conversion into lower boiling hydrocarbons and produce anexchange reaction between benzene and higher boiling hcmologs thereof tothereby consume benzene and effect selective conversion to toluene,directing the resultant products of conversion to a fractionating zonewherein the products are fractionated to separate fractions comprisingbenzene, toluene, xylene and higher boiling hydrocarbons. directing thehigher boiling hydrocarbons to a second conversion zone wherein thehydrocarbons are subiected to catalytic cracking in contact with ametallic fluoride to effectconversionto lower boiling hydrocarbons,directing the resultant products of conversion to said fractionatingzone and recycling the benzene and xylene fractions to the firstmentioned conversion zone.

' 5. In the manufacture of toluene the process that comprises subjectinga mixture of benzene and petroleum naphtha containing aro-' matichydrocarbons to conversion in a conversion zone in contact with acatalyst comprising a synthetic composite of precipitated silica andalumina at a temperature of the order of 800l000 F. to thereby effectconversion into lower boiling hydrocarbons and effect an exchangereaction between benzene and higher boiling homolog thereof to produce anet con-.

sumption of benzene and a selective formation of toluene with a netreduction in aromatichydrocarbons higher boiling than the xylenes,fractionating the resultant products of conversion in a fractionatingzone to separate fractions comprising benzene, toluene and xylenes fromhigher boiling hydrocarbons, directing said higher boiling hydrocarbonsto a second conversion zone wherein the hydrocarbons are subjected toconversion temperature in contact with a cracking catalyst to effectconversion into lower boiling hydrocarbons, directing the resultantproducts of conversion from the latter conversion zone to saidfractionating zone and recycling the benzene fraction to thefirst-mentioned conversion zone.

6. In the manufactureof toluene the process that comprises subjecting amixture of benzene and petroleum naphtha containing aromatichydrocarbons to conversion in a conversion zone in contact with acatalyst comprising a synthetic composite of precipitated silica andalumina at a temperature of the order of 800-1000 F. to thereby eflectconversion into lower boiling h8- drocarbon and eifect an exchangereaction between benzene and higher boiling homologs thereof to producea net consumption of benzene and a selective formation of toluene with anet reduction in aromatic hydrocarbons higher boiling than the xylenes,fractionating the resultant products of conversion in a fractionatingzone to separate benzene, toluene and xylene fractions from higherboiling hydrocarbons, directing said higher boiling hydrocarbons to asecond conversion zone wherein the hydrocarbons are subjected toconversion temperature in contact with a cracking catalyst to effectconversion into lower boiling hydrocarbons, directing the resultantproducts of conversion from the latter conversion zone to saidfractionating zone and cycling the benzene and xylene fractions to thefirst-mentioned conversion zone.

GEORGE B. ARNOLD.

